large umbrella with a long handle, used for street stalls
簦 centers on a large, long-handled umbrella, especially the kind used to cover street stalls. It is a specific object rather than a broad concept.
簦 combines 竹 (bamboo) with 登, which likely contributes the sound. The character refers to a bamboo umbrella, consistent with the bamboo radical.
The bamboo top 竹 over 登 suggests a tall bamboo frame rising up: a large umbrella on a long handle, perfect for a street stall.
For トウ, picture a tall umbrella over a street stall, and think of the stall owner calling out 'Toh!' as they open it: Toh -> トウ.